The present invention relates to a free radical process for preparing radial polymers, radial polymers prepared by the process, additive concentrates and lubricating oil compositions.
The viscosity of oils of lubricating viscosity is generally dependent upon temperature. As the temperature of the oil is increased, the viscosity usually decreases, and as the temperature is reduced, the viscosity usually increases.
The function of a viscosity improver is to reduce the extent of the decrease in viscosity as the temperature is raised or to reduce the extent of the increase in viscosity as the temperature is lowered, or both. Thus, a viscosity improver ameliorates the change of viscosity of an oil containing it with changes in temperature. The fluidity characteristics of the oil are improved.
Viscosity improvers are usually polymeric materials and are often referred to as viscosity index improvers. Many viscosity improvers are block copolymers.
Dispersants are also well-known in the lubricating art. Dispersants are employed in lubricants to keep impurities, particularly those formed during operation of mechanical devices such as internal combustion engines, automatic transmissions, etc. in suspension rather than allowing them to deposit as sludge or other deposits on the surfaces of lubricated parts.
Multifunctional additives that provide both viscosity improving properties and dispersant properties are likewise known in the art. Such products are described in numerous publications including Dieter Klamann, xe2x80x9cLubricants and Related Productsxe2x80x9d, Verlag Chemie Gmbh (1984), pp 185-193; C. V. Smalheer and R. K. Smith xe2x80x9cLubricant Additivesxe2x80x9d, Lezius-Hiles Co. (1967); M. W. Ranney, xe2x80x9cLubricant Additivesxe2x80x9d, Noyes Data Corp. (1973), pp 92-145, M. W. Ranney, xe2x80x9cLubricant Additives, Recent Developmentsxe2x80x9d, Noyes Data Corp. (1978), pp 139-164; and M. W. Ranney, xe2x80x9cSynthetic Oils and Additives for Lubricantsxe2x80x9d, Noyes Data Corp. (1980), pp 96-166. Each of these publications is hereby expressly incorporated herein by reference.
Dispersant-viscosity improvers are generally prepared by functionalizing, i.e., adding polar groups, to a hydrocarbon polymer backbone.
Hayashi, et al, U.S. Pat. No. 4,670,173 relates to compositions suitable for use as dispersant-viscosity improvers made by reacting an acylating reaction product which is formed by reacting a hydrogenated block copolymer and an alpha-beta olefinically unsaturated reagent in the presence of free-radical initiators, then reacting the acylating product with a primary amine and optionally with a polyamine and a mono-functional acid.
Chung et al, U.S. Pat. No. 5,035,821 relates to viscosity index improver-dispersants comprised of the reaction products of an ethylene copolymer grafted with ethylenically unsaturated carboxylic acid moieties, a polyamine having two or more primary amino groups or polyol and a high functionality long chain hydrocarbyl substituted dicarboxylic acid or anhydride.
Van Zon et al, U.S. Pat. No. 5,049,294, relates to dispersant/VI improvers produced by reacting an alpha, beta-unsaturated carboxylic acid with a selectively hydrogenated star-shaped polymer then reacting the product so formed with a long chain alkane-substituted carboxylic acid and with a C1 to C18 amine containing 1 to 8 nitrogen atoms and/or with an alkane polyol having at least two hydroxy groups or with the performed product thereof.
Bloch et al, U.S. Pat. No. 4,517,104, relates to oil soluble viscosity improving ethylene copolymers reacted or grafted with ethylenically unsaturated carboxylic acid moieties then with polyamines having two or more primary amine groups and a carboxylic acid component or the preformed reaction product thereof.
Gutierrez et al, U.S. Pat. No. 4,632,769, describes oil-soluble viscosity improving ethylene copolymers reacted or grafted with ethylenically unsaturated carboxylic acid moieties and reacted with polyamines having two or more primary amine groups and a C22 to C28 olefin carboxylic acid component.
Each of these patents is hereby expressly incorporated herein by reference.
For additional disclosures concerning multi-purpose additives and particularly viscosity improvers and dispersants, the disclosures of the following United States patents are incorporated herein by reference:
U.S. Pat. No. 5,530,079, Veregin et al., discloses a polymerization process comprising heating a mixture of a free radical initiator, a stable free radical agent, at least one polymerizable monomer compound, and optionally a solvent.
U.S. Pat. No. 5,401,804, Georges et al., discloses a free radical polymerization process comprising heating a mixture of a free radical initiator, a stable free radical agent, and at least one polymerizable monomer. The stable free radical agent includes nitroxide free radicals. An organic sulfonic or carboxylic acid can be added to increase the rate of polymerization.
U.S. Pat. No. 3,189,663, Nozaki, discloses block copolymers comprising copolymers where the macromolecules are made up of at least two different linear segments. The first is made up of a linear polymer of a member of the group consisting of ethylenically unsaturated carboxylic acids, anhydrides thereof, and their esters and amides. The second segment is made up of a polymer of a dissimilar member of the first group, esters of unsaturated alcohols and saturated acids, alkenes, alkadienes, vinyl halides, vinyl substituted aromatic hydrocarbons, alkenyl-substituted halo-hydrocarbons, and alkenyl ethers.
U.S. Pat. No. 4,581,429, Solomon et al., discloses a process for free radical polymerization to produce relatively short chain length homo- and copolymers. The initiator has the general formula 
U.S. Pat. No. 5,608,023, Odell et al., discloses a polymerization process comprising heating a mixture of a free radical initiator, a stable free radical agent, at least one polymerizable monomer compound, and a sulfonic acid salt polymerization rate enhancing compound to form thermoplastic resins.
U.S. Pat. No. 5,449,724, Moffatt et al., discloses a free radical polymerization process which includes heating a mixture comprised of a free radical initiator, a stable free radical agent, and ethylene.
U.S. Pat. No. 5,677,388, Koster et al., relates to a living free-radical polymerization process for preparing polymers from vinyl aromatic monomers comprising polymerizing the vinyl aromatic monomer in the presence of a difunctional nitroxyl initiator.
U.S. Pat. No. 4,180,530, Bi et al., describe star-block copolymers containing 60 to 95 percent by weight of a monovinyl aromatic compound and 40 to 5 percent by weight of a conjugated diene having 4 to 8 carbon atoms. The copolymers have the general formula (A-Axe2x80x2/B-Bxe2x80x2)m-X-(Bxe2x80x2-B/Axe2x80x2)n where A is a non-elastomeric polymer segment based on 80 to 90 percent by weight of the total monovinyl aromatic compound, B/Axe2x80x2 or Axe2x80x2B is an elastomeric copolymer segment based on a random copolymer of the monovinyl aromatic compound and the conjugated diene, Bxe2x80x2 is an elastomeric segment of poly (conjugated diene) containing 20-40 percent by weight of the total conjugated diene, m and n are integers whose sum is between 3 and 20, and X is the radical of a polyfunctional coupling agent forming the nucleus of the star-block copolymer. These are prepared by a four-stage process of anionic polymerization.
U.S. Pat. No. 5,496,898, Sutherland et al., describe star polymers prepared by an anionic process having polymeric arms of a hydrogenated conjugated diene and substantially smaller polymeric arms of a methacrylate used as viscosity improvers. Methacrylate groups can be converted to amide or imide groups by reaction with primary or secondary amine to afford dispersant properties.
U.S. Pat. No. 5,723,511, Kazmaier et al., describes a process for the preparation of branched thermoplastic resins comprising: heating a mixture of a free radical initiator, at least one first free radical reactive monomer, at least one free radical reactive branching agent compound, and at least one stable free radical agent, to produce a linear or unbranched polymer product with a free radical initiator fragment at one end and a covalently bonded stable free radical agent at the other end of the polymerized chain of monomers; and irradiating the unbranched polymer product in the presence of a reactive compound selected from the group consisting of a free radical reactive monomer, a branching agent compound, and mixtures thereof to form a branched polymeric product.
Rhodes et al. in U.S. Pat. No. 5,460,739, describes star polymers which can be used as viscosity index improvers in oil compositions. The star polymers are made by an anionic process, and have triblock copolymer arms of hydrogenated polyisoprene-polybutadiene-polyisoprene.
Rhodes et al., in U.S. Pat. No. 5,458,791, describes star polymers used as viscosity index improvers in oil compositions formulated for high performance engines. The star polymers have specific triblock copolymer arms of hydrogenated polyisoprene-polystyrene-polyisoprene.
Storey et al. in U.S. Pat. No. 5,458,796, relates to the synthesis of star polymers containing polyisobutylene (PIB) via the arm-first, core-last method by a cationic process. These star polymers are used as viscosifiers for lubricating oils due to their inherent lack of unsaturation and their relatively flat temperature/viscosity profiles.
An object of this invention is to provide a novel process for preparing radial polymers.
Another object is to provide a one-pot, relatively short duration process for preparing radial polymers.
Another object is to provide radial polymers which may be isolated as diluent-free, dry, free-flowing solids.
Another object of this invention is to provide novel radial polymers useful as lubricant additives.
Still another object is to provide lubricants having improved shear stability and viscometric properties.
A more specific object is to provide additives directed to improving lubricant viscometrics.
Another object is to provide viscosity improvers having high thickening efficiency.
Other objects will in part be obvious in view of this disclosure and will in part appear hereinafter.
The present invention provides a process for preparing radial polymers comprising at least 3 polymeric arms and a central core comprising a polymerized di- or polyfunctional monomer, said process comprising the steps,
(a) polymerizing at an elevated temperature, a charge comprising at least one free radical-polymerizable monomer to prepare a stabilized active polymer block (A) using a free radical polymerization process,
wherein a stable free radical agent is employed during the polymerization, thereby preserving the stabilized active polymerization site at the terminus of the polymer; optionally
(b) adding at least one additional free radical-polymerizable monomer, at least one of which is different from the monomers making up the first charge of monomers, to the stabilized active polymer block (A); and further reacting the mixture using a free radical process to effect copolymerization of said monomers, thereby preparing an A-B block copolymer having a stabilized active polymerization site at the terminus of the polymer; then
(c) adding at least one coupling agent comprising a polyfunctional monomer and reacting the stabilized active polymers from (a) or (b) with the coupling agent to form a radial polymer.
The present invention also relates to radial polymers, including radial block copolymers prepared by the above process, additive concentrates for preparing lubricating oil compositions and lubricating oil compositions. In other embodiments, the present invention relates to radial block copolymers having more than two blocks.
As used herein, the terms xe2x80x9chydrocarbonxe2x80x9d, xe2x80x9chydrocarbylxe2x80x9d or xe2x80x9chydrocarbon basedxe2x80x9d mean that the group being described has predominantly hydrocarbon character within the context of this invention. These include groups that are purely hydrocarbon in nature, that is, they contain only carbon and hydrogen. They may also include groups containing substituents or atoms which do not alter the predominantly hydrocarbon character of the group. Such substituents may include halo-, alkoxy-, nitro-, etc. These groups also may contain hetero atoms. Suitable hetero atoms will be apparent to those skilled in the art and include, for example, sulfur, nitrogen and oxygen. Therefore, while remaining predominantly hydrocarbon in character within the context of this invention, these groups may contain atoms other than carbon present in a chain or ring otherwise composed of carbon atoms provided that they do not adversely affect reactivity or utility of the process or products of this invention.
In general, no more than about three non-hydrocarbon substituents or hetero atoms, and preferably no more than one, will be present for every 10 carbon atoms in the hydrocarbon or hydrocarbon based groups. Most preferably, the groups are purely hydrocarbon in nature, that is, they are essentially free of atoms other than carbon and hydrogen.
Throughout the specification and claims the expression oil soluble or dispersible is used. By oil soluble or dispersible is meant that an amount needed to provide the desired level of activity or performance can be incorporated by being dissolved, dispersed or suspended in an oil of lubricating viscosity. Usually, this means that at least about 0.001% by weight of the material can be incorporated into a lubricating oil. For a further discussion of the terms oil soluble and dispersible, particularly xe2x80x9cstably dispersiblexe2x80x9d, see U.S. Pat. No. 4,320,019 which is expressly incorporated herein by reference for relevant teachings in this regard.
The expression xe2x80x9clowerxe2x80x9d is used throughout the specification and claims. As used herein to describe various groups, the expression xe2x80x9clowerxe2x80x9d is intended to mean groups containing no more than 7 carbon atoms, more often, no more than 4, frequently one or two carbon atoms.
It must be noted that as used in this specification and appended claims, the singular forms also include the plural unless the context clearly dictates otherwise. Thus the singular forms xe2x80x9caxe2x80x9d, xe2x80x9canxe2x80x9d, and xe2x80x9cthexe2x80x9d include the plural; for example xe2x80x9ca monomerxe2x80x9d includes mixtures of monomers of the same type. As another example the singular form xe2x80x9cmonomerxe2x80x9d is intended to include both singular and plural unless the context clearly indicates otherwise.
Thickening efficiency (abbreviated herein as xe2x80x9cTExe2x80x9d) is defined herein as a measure of the thickening power of a polymeric viscosity improver in a given base oil. It is expressed a the difference of the logarithm of the viscosity at 100xc2x0 C. in centistokes of the polymer containing lubricant and the logarithm of the viscosity at 100xc2x0 C. in centistokes of the base oil alone, divided by the concentration (as a decimal fraction) of the polymer in the lubricant.
In the context of this invention the term xe2x80x9cpolymerxe2x80x9d refers to a polymer of any type including homopolymers and copolymers. The term xe2x80x9ccopolymerxe2x80x9d means a polymer derived from two or more different monomers. Thus, a polymer derived from a mixture of, for example, methyl-, butyl-, C9-11-, and C12-18- methacrylates, or a polymer having two or more distinct blocks, is a copolymer as defined herein. The polymers of this invention also may contain units derived from nitrogen-containing monomers.
The expression xe2x80x9csubstantially inertxe2x80x9d is used in reference to diluents. When used in this context, xe2x80x9csubstantially inertxe2x80x9d means the diluent is essentially inert with respect to any reactants or compositions of this invention, that is, it will not, under ordinary circumstances, undergo any significant reaction with any reactant or composition, nor will it interfere with any reaction or composition of this invention.
The expression viscosity index (often abbreviated VI), is frequently used herein. Viscosity index is an empirical number indicating the degree of change in viscosity within a given temperature range. A high VI signifies an oil that displays a relatively small change in viscosity with temperature.
The polymers of this invention may be derived from a wide variety of monomers including styrene and substituted styrenes, xcex1,xcex2-unsaturated carboxylic acids, for example maleic, fumaric, itaconic, acrylic, methacrylic, cyanoacrylic, and esters, anhydrides, and amides thereof, and free radical polymerizable olefins and conjugated dienes. Especially preferred monomers are vinyl substituted aromatic compounds and acrylic monomers as described in greater detail hereinbelow.
As noted above, the radial polymers of the invention are prepared by first generating stabilized polymers which are further reacted with a coupling agent to form a radial polymer. Thus, the stabilized polymers become the arms of the radial polymer.
The radial polymer will contain at least 3 polymeric arms, often from 3 to about 10 and typically from 5 to about 8 arms. Generally, the radial polymers of this invention contain no more than 15, more often no more than 10, and usually no more than 8 polymeric arms.
The arms of the radial polymer may be essentially identical or may comprise different compositions.
As noted above, each polymeric arm may be a homopolymer or a copolymer. When the arm is copolymeric, it is often a block copolymer but may be a random or alternating copolymer.
Homopolymeric arms are prepared according to step (a) of the above-described process, wherein a single monomer is employed.
Copolymeric arms may be generated by the process employing only step (a) wherein two or more monomers are polymerized simultaneously forming, for example, statistical copolymers, alternating copolymers, etc.
Copolymeric arms which are block copolymers are prepared according to the procedure wherein both steps (a) and (b) are employed, i.e., they are A-B block copolymers.
Copolymeric arms may also be tri- and higher- block copolymers.
A-B-A block copolymers may be prepared by incorporating an additional A-block by (e) after step (b) and before step (c), adding and polymerizing, at an elevated temperature, at least one additional monomer wherein said additional monomer has the same composition as that charged to generate block A.
A C-block may be incorporated by (f) after step (b) and before step (c) adding and polymerizing at an elevated temperature, at least one free radical-polymerizable monomer wherein the composition of the monomer is different from the monomers employed in steps (a)-(b).
Higher block copolymers may be prepared by analogous means.
The Vinyl Aromatic Monomer
In the present invention one of the monomers may be a vinyl substituted aromatic compound.
The vinyl substituted aromatics generally contain from 8 to about 20 carbons, preferably from 8 to 12 carbon atoms and most preferably, 8 or 9 carbon atoms. Heterocyclic compounds having, for example sulfur, oxygen or nitrogen ring heteroatoms, such as vinyl pyridines are contemplated.
Examples of vinyl substituted aromatics include vinyl anthracenes, vinyl naphthalenes and vinyl benzenes (styrenes) including substituted styrenes. Substituted styrenes include styrenes that have substituents on the ring or on the vinyl group. Such substituents include halo-, amino-, alkoxy-, carboxy-, hydroxy-, sulfonyl-, hydrocarbyl- wherein the hydrocarbyl group has from 1 to about 12 carbon atoms, and other substituents. Examples of styrenes include styrene, alpha-lower alkyl substituted styrene, for example, alpha-methyl styrene and alpha-ethyl styrene, styrenes having ring substituents, preferably, lower alkyl ring substituents, for example, ortho-methyl styrene, meta-methyl styrene, para-methyl styrene, and para-tertiary-butylstyrene, vinyl benzene sulfonic acid, and para-lower alkoxy styrene. Mixtures of two or more vinyl aromatic monomers can be used. Styrene and substituted styrenes are preferred.
The Acrylic Monomer
As used herein the term xe2x80x9cacrylic monomerxe2x80x9d includes acrylic acids, esters of acrylic acids, acrylic amides, and acrylonitriles and the corresponding alkacryl-, especially methacryl-, compounds, particularly alkyl methacrylates, methacrylamides, and methacrylonitrile. The esters of acrylic acids typically contain from 2 to about 50 carbon atoms in the ester group, which ester group includes the carbonyl carbon atom. Often, the ester groups are lower alkyl esters, wherein the expression xe2x80x9clower alkylxe2x80x9d means alkyl groups having no more than 7 carbon atoms, preferably from 1 to about 4 carbons. In another preferred embodiment, the ester group contains from 2 to about 30 carbon atoms, preferably from about 9 to about 23 carbon atoms, often from about 8 to about 18 carbon atoms. In an especially preferred embodiment, the ester group contains a mixture of alkyl groups, such as from about 9 to about 11 carbon atoms or from about 13 to about 16 carbon atoms.
Examples of useful acrylic monomers include acrylic acid, methacrylic acid, esters thereof, including lower alkyl esters, fatty esters, and mixed esters, such as C8-10 alkyl esters and C12-15 alkyl esters, acrylamide, methacrylamide, and N- and N,N- substituted acrylamides and the corresponding methacrylamides, acrylonitrile and methacrylonitrile.
Also included among xe2x80x9cacrylicxe2x80x9d monomers are xcex1,xcex2-unsaturated polycarboxylic monomers such as maleic acid, esters thereof, amides, amidic acids and esters thereof, and the corresponding fumaric compounds.
Stable Free Radical Agent
Stable free radical agents are known. Suitable stable free radical agents include phenoxy radicals and nitroxy radicals. Examples of phenoxy radicals include phenoxy radicals substituted in the 2 and 6 positions by bulky groups such as tert-alkyl (e.g., t-butyl), phenyl, or dimethylbenzyl, and optionally substituted at the 4 position by an alkyl, alkoxyl, aryl, or aryloxy group or by a heteroatom containing group (e.g., S, N, or O) such as a dimethylamino or diphenylamino group, and materials which contain two or more such aromatic rings bridged at, e.g., the 4 position. Thiophenoxy radical analogs of such phenoxy radicals are also contemplated. Typical stable nitroxy radicals are those having the general formula R1R2Nxe2x80x94Oxe2x80xa2, where R1 and R2 are tertiary alkyl groups, or where R1 and R2 together with the N atom form a cyclic structure, preferably having tertiary branching at the positions alpha to the N atom. Examples of hindered nitroxy radicals include 2,2,5,5-tetraalkylpyrrolidinoxyl radicals, as well as those in which the 5-membered heterocycle ring is fused to an alicyclic or aromatic ring, hindered aliphatic dialkylaminoxyl and iminoxyl radicals such as (R3C)2Nxe2x80x94Oxe2x80xa2 and R2Cxe2x95x90Nxe2x80x94Oxe2x80xa2, diarylaminoxyl and aryl-alkylaminoxyl radicals such as the nitroxyl radical from alkyl diphenylamine, (Rxe2x80x94Ar)2Nxe2x80x94Oxe2x80xa2, nitroxyl derivatives of dihydroquinoline light stabilizers and antiozonants (available from Ciba-Geigy), in monomeric and polymeric forms, and nitroxyl radicals derived from dibenzo-heterocycles such as phenothiazines and phenoxazines. A specific, preferred example is 2,2,6,6-tetramethyl-1-piperidinyloxy, which is available from Aldrich Chemical Company under the trade name TEMPO(trademark). This material is understood to be a representative of materials of the general structure 
where each R is independently alkyl or aryl, Rxe2x80x2 is hydrogen, alkyl, or aryl, X is hydrogen, alkyl, aryl, alkoxyl, carbalkoxy, carboxyalkyl, carboxamido- (xe2x80x94NHC(O)-lower alkyl), or chloro, or where Rxe2x80x2 is absent and X is xe2x95x90O, xe2x95x90N, or xe2x95x90S. Esters and ethers thereof are also contemplated.
Hindered amine stabilizers are described in detail in Polymer Stabilization and Degradation, P. P. Klemchuk, Editor, American Chemical Society, Symposium Series 280, 1985, pages 55-97. These materials are closely related structurally to nitroxy radicals and can be converted thereinto by known means. Accordingly, the hindered amine structures illustrated in particular on pages 56, 58, 61, 91, 92, 94, 95, 97, and 97 of the above-cited document can be taken as illustrative of characteristic structures of a variety of stable nitroxy radicals.
The amount of stable free radical agent employed in the polymerization of the first block is typically 0.001 to 0.01 moles per mole of monomer, particularly for polymer molecular weights in the range of 10,000 to 100,000. Specific amounts can readily be determined and appropriately adjusted by the person skilled in the art.
Free Radical Initiators
Free radical initiators include peroxy compounds, peroxides, hydroperoxides, and azo compounds which decompose thermally to provide free radicals.
Free radical generating reagents are well know to those skilled in the art. Examples include benzoyl peroxide, t-butyl perbenzoate, t-butyl metachloroperbenzoate, t-butyl peroxide, sec-butylperoxydicarbonate, azobisisobutyronitrile, and the like. Numerous examples of free radical-generating reagents, also known as free-radical initiators, are mentioned in the above-referenced texts by Flory and by Bovey and Winslow. An extensive listing of free-radical initiators appears in J. Brandrup and E. H. Immergut, Editor, xe2x80x9cPolymer Handbookxe2x80x9d, 2nd edition, John Wiley and Sons, New York (1975), pages II-1 to II-40. Preferred free radical-generating reagents include t-butyl peroxide, t-butyl hydroperoxide, t-amyl peroxide, cumyl peroxide, t-butyl peroctoate, t-butyl-m-chloroperbenzoate and azobisisovaleronitrile.
The free radical initiators are generally used in an amount from 0.01 to about 10 percent by weight based on the total weight of the reactants. Preferably, the initiators are used at about 0.05 to about 2 percent by weight. The molar ratio of free radical initiator to stable free radical agent is from about 0.2 to about 2:1, preferably from about 0.8:1 to about 1.2:1, even more often from about 1.1 to 1.2:1, frequently 0.8-0.9:1.
The reaction is usually conducted at temperatures ranging between about 80xc2x0 C. to about 200xc2x0 C., preferably between about 130xc2x0 C. to about 170xc2x0 C. Considerations for determining reaction temperatures include reactivity of the system and the half-life of the initiator at a particular temperature.
The choice of free radical generating reagent can be an important consideration. For example, when the reaction is conducted with a solvent such as a hydrocarbon oil, grafting of monomer onto the oil diluent may occur. It has been observed that the choice of initiator affects the extent of grafting of the monomer onto the oil diluent. Reducing the amount of monomer grafted onto the diluent usually results in an increased amount of monomer incorporated into the polymer block.
Promoter
To further facilitate the polymerization, the polymerization can be conducted in the presence of a strong acid or an amine salt of an acid in an amount suitable to enhance the rate of polymerization, that is to say, a catalytic amount. Such an acid will normally have a pKa as measured in water of less than 4, preferably less than 2.5, and more preferably less than 2. A preferred amount of the acid or amine salt is an amount sufficient to reduce the pH of the reaction medium to 4 to 5. Otherwise stated, the ratio of an organic acid to the amount of the sterically hindered stable free radical is preferably about 1:1 to about 1:20, often to about 1:11 by weight. Either organic or inorganic acids can be used, for example mineral acids, sulfonic acids, acidic clays, organic sulfonic acids, carboxylic acids, acidic salts of any of these acids, and monoesters of sulfurous- and sulfuric acids. Preferred acids include carboxylic acids, sulfonic acids, phosphonic acids, and phosphoric acids. One such acid which has been successfully employed in the past is camphorsulfonic acid. See, for instance, U.S. Pat. No. 5,401,804. Other feasible acids include methane sulfonic acid, toluene sulfonic acid, sulfonic acid functionalized resins, 2-fluoro-1-methylpyridinium p-toluenesulfonate, trifluoromethanesulfonic acid, 3,5-di-t-butyl-4-hydroxybenzenesulfonic acid, and pyridinium p-toluenesulfonate.
The medium for polymerization is not particularly critical and can be any such medium in which polymerization can be effected. Alternatively, polymerization can be conducted in the substantial absence of medium or solvent, that is, neat. Preferably, the medium is one in which the reactants are soluble, often a substantially inert normally liquid organic diluent. Examples include alkyl aromatics, preferably in relatively small amounts so that a relatively high concentration of monomer can be maintained. If such a medium is used, it should also be one from which an initially formed block can be separated, such as by filtration, precipitation into a nonsolvent, or evaporation of the medium. Thus, a first block can be isolated prior to the further reaction to prepare a second block, while retaining the active polymerization site thereon. This retention of the active polymerization site is a characteristic and a benefit of the use of the stabilized free radical initiator. Solvents which readily transfer hydrogen atoms under radical conditions are preferably avoided. For best results in retaining the active polymerization site, processing of the polymer in the presence of hydrogen atom transfer agents, particularly at elevated temperatures, should be avoided.
Alternatively, the process to prepare subsequent blocks may be conducted without isolation of the preceding block.
The polymerization of monomers to prepare a second block can be accomplished either with or without employing additional free radical initiator and or promoter. Often, additional promoter or initiator is beneficial, and sometimes is necessary, to enable polymerization of the second block to proceed, especially at an acceptable rate.
In the process to prepare an A-B block copolymer, the weight ratio of a first monomer to a second, different, monomer, typically ranges from about 20:1 to about 1:20, preferably, from about 5:1 to about 1:10, most preferably from about 35:65 to about 65:35.
In the process of this invention to prepare arms having A-B block configuration, from about 5 to about 95 mole % of the charge comprising the at least one free radical polymerizable monomer, preferably, from about 50 to about 80 mole %, is polymerized to prepare the stabilized active polymer block (A). To the mixture of A-block polymer and unreacted monomer is then added the at least one additional free radical polymerizable monomer, at least one of which is different from the monomers making up the first charge of monomers, which is then further reacted to form a (B) block. Optionally, additional free radical initiator and/or promoter may be utilized.
The polymerization process may be halted by (d) reducing the temperature below the polymerization temperature of the monomers. The polymer may then be further worked up and isolated as a substantially solvent free dry polymer by stripping off diluent, if any, and volatile unreacted monomer, or by precipitation of the polymer from a solvent in which the polymer has limited solubility, and which solvent selectively takes up unreacted monomer.
Additional blocks may be incorporated into the polymeric arms of this invention.
In one embodiment, an additional (A) block is made up of the same monomers employed to generate the first block, block (A). The additional block is incorporated by (e) after step (b) and before step (c), adding and polymerizing, at an elevated temperature, at least one additional vinyl aromatic monomer wherein said additional vinyl aromatic monomer has the same composition as that charged to generate block A. In this embodiment, the amount of monomers charged to generate the additional block ranges from about 0.2 to about 5 times that used to prepare the first (A) block. The additional monomer is charged and polymerized, optionally with additional free-radical initiator, in the same fashion as the preparation of the (B) block. The resulting polymer is an A-B-A triblock polymer.
In another embodiment, the additional block is a (C) block made up of monomers wherein the composition of the third monomers is different from those employed in steps (a) and) (b) to generate the (A) and (B) blocks. This additional block is incorporated by (f) after step (b) and before step (c) adding and polymerizing at an elevated temperature, at least one free radical polymerizable monomer wherein the composition of the third monomer is different from the monomers employed in steps (a)-(b). The additional monomers are charged and polymerized, optionally with additional free-radical initiator. The resulting polymer is an A-B-C triblock polymer. The weight ratio of the monomers charged to prepare the additional block to the total weight of monomers charged to prepare the (A) and (B) blocks ranges from about 1:5 to about 10:1.
In a preferred embodiment, the monomers are at least one of vinyl aromatic monomers and acrylic monomers. The vinyl aromatic monomer is preferably selected from the group consisting of styrenes comprising at least one of styrene, an xcex1- lower alkyl substituted styrene, vinyl benzene sulfonic acid, and styrenes having C1-4 alkyl ring substituents, and the acrylic monomer is preferably selected from the group consisting of acrylic acids, esters of acrylic acids, preferably those containing from 2 to about 50 carbon atoms in the ester group, acrylic amides, and acrylonitriles. Especially preferred is wherein the styrenes comprise styrene and the acrylic monomer comprises at least one methacrylic acid ester, especially an aliphatic ester containing from 9 to about 23 carbon atoms in the ester groups.
The process of this invention is conducted to provide polymeric arms having weight average molecular weights ({overscore (M)}w) ranging from about 1,000, more often from about 3,000, even more often from about 5,000 to about 500,000, often from about 10,000 to about 250,000 frequently up to about 25,000, frequently from about 3,000 to about 25,000, often up to about 15,000. In another embodiment, the resulting block copolymer has weight average molecular weight ranging from about 5,000 to about 250,000, often up to about 150,000, frequently up to about 100,000.
The molecular weight of a polymeric arm is the total of the molecular weights of the monomeric components, or for a block copolymer, the individual blocks. In a preferred embodiment, the {overscore (M)}w of the A-block ranges from about 4,000 to about 80,000 and the {overscore (M)}w of the B-block ranges from about 4,000 to about 80,000. Preferred A:B weight ratios are 1:1 up to 2:1, preferably up to about 1.5:1. Molecular weights of the B-block and of third blocks are determined by subtracting the molecular weight of the A-block or for polymers containing more than two blocks, the total molecular weight of the previously prepared blocks, from the total molecular weight of the polymer.
As noted hereinabove, the block copolymeric arms of this invention may comprise a third block. When the block copolymer is a triblock copolymer, the molecular weight of the third block typically ranges from about 4,000 to about 80,000.
Specific molecular weights of polymeric arms are frequently dictated by the intended use. For the copolymers of this invention, when the polymer is intended to be used in gear lubricants, preferred {overscore (M)}w for each block range from about 5,000 to about 20,000, preferably up to about 12,000, with the preferred A-block to B-block {overscore (M)}w ratio of about 1-1.4:1. For use in hydraulic oils and in automatic transmission fluids, typical molecular weights range from about 10,000 to about 30,000, preferably up to about 20,000. For engine oils, for example for gasoline passenger car engines and for heavy duty diesel engines, the molecular weight for each block frequently ranges from about 40,000 to about 100,000, often up to about 80,000.
Molecular weights of the polymers are determined using well known methods described in the literature. Examples of procedures for determining the molecular weights are gel permeation chromatography (GPC) (also known as size-exclusion chromatography), light scattering, and vapor phase osmometry (VPO). The GPC technique employs standard materials against which the samples are compared. For best results, standards that are chemically similar to those of the sample are used. For example, for polystyrene polymers, a polystyrene standard, preferably of similar molecular weight, is employed. When standards are dissimilar to the sample, generally relative molecular weights of related polymers can be determined. For example, using a polystyrene standard, relative, but not absolute, molecular weights of a series of polymethacrylates may be determined. These and other procedures are described in numerous publications including:
P. J. Flory, xe2x80x9cPrinciples of Polymer Chemistryxe2x80x9d, Cornell University Press (1953), Chapter VII, pp 266-316, and
xe2x80x9cMacromolecules, an Introduction to Polymer Sciencexe2x80x9d, F. A. Bovey and F. H. Winslow, Editors, Academic Press (1979), pp 296-312.
W. W. Yau, J. J. Kirkland and D. D. Bly, xe2x80x9cModern Size Exclusion Liquid Chromatographyxe2x80x9d, John Wiley and Sons, New York, 1979.
Radial polymers of this invention may be prepared by reacting the foregoing polymeric compositions with a coupling agent comprising a polyfunctional monomer. As noted above, the arms of the radial polymer may be substantially the same or may be different.
When the arms are substantially the same, the coupling agent is reacted with stabilized polymers that are substantially the same, that is, all the same homopolymer or copolymeric composition.
When the arms are different, the coupling agent may be reacted with a mixture of different stabilized monomers.
The Coupling Agent
A variety of coupling agents are useful for preparing the radial polymers of this invention. The coupling agents are polyfunctional monomers. The polymeric, stabilized free radical sites can add to one of the polymerizable vinyl groups of the coupling agent, then the adduct can undergo further polymerization through the remaining sites to form a radial polymer.
Examples of useful coupling agents include divinyl benzene, glycol bis-acrylates or methacrylates, polyol acrylates and methacrylates, and alkylene bis-acrylamides.
While not wishing to be bound by theory, it is proposed that the radial polymers of this invention are formed by a stepwise process: 
where T=stabilizing agent. It is also believed that individual radial polymers can couple to form very high molecular weight polymers.